Chloride/proton exchange by the lysosomal anion transporter ClC-7/Ostm1 is of pivotal importance for the physiology of lysosomes and bone resorption. Mice lacking either ClC-7 or Ostm1 develop a lysosomal ... [more ▼]

Chloride/proton exchange by the lysosomal anion transporter ClC-7/Ostm1 is of pivotal importance for the physiology of lysosomes and bone resorption. Mice lacking either ClC-7 or Ostm1 develop a lysosomal storage disease and mutations in either protein have been found to underlie osteopetrosis in mice and humans. Some human disease-causing CLCN7 mutations accelerate the usually slow voltage-dependent gating of ClC-7/Ostm1. However, it has remained unclear whether the fastened kinetics is indeed causative for the disease. Here we identified and characterized a new deleterious ClC-7 mutation in Belgian Blue Cattle with a severe symptomatology including peri-natal lethality and in most cases gingival hamartomas. By autozygosity mapping and genome-wide sequencing we found a handful of candidate variants, including a cluster of three private SNPs causing the substitution of a conserved tyrosine in the CBS2 domain of ClC-7 by glutamine. The case for ClC-7 was strengthened by subsequent examination of affected calves that revealed severe osteopetrosis. The Y750Q mutation largely preserved the lysosomal localization and assembly of ClC-7/Ostm1, but drastically accelerated its activation by membrane depolarization. These data provide first evidence that accelerated ClC-7/Ostm1 gating per se is deleterious, highlighting a physiological importance of the slow voltage-activation of ClC-7/Ostm1 in lysosomal function and bone resorption. [less ▲]

Innate regulatory networks within organs maintain tissue homeostasis and facilitate rapid responses to damage. We identified a novel pathway regulating vessel stability in tissues involving matrix metalloproteinase 14 (MMP14) and transforming growth factor beta (TGFbeta)1. Whereas plasma proteins rapidly extravasate out of vasculature in wildtype mice following acute damage, short-term treatment of mice in vivo with a broad-spectrum metalloproteinase inhibitor, neutralizing antibodies to TGFbeta1 or an ALK5 inhibitor significantly enhanced vessel leakage. In contrast, in a mouse model of age-related dermal fibrosis where MMP14 activity and TGFbeta bioavailability are chronically elevated, or in mice that ectopically express TGFbeta in epidermis, cutaneous vessels are resistant to acute leakage. Characteristic responses to tissue damage are reinstated if fibrotic mice are pre-treated with metalloproteinase inhibitors or TGFbeta signaling antagonists. Neoplastic tissues on the other hand are in a constant state of tissue damage and exhibit altered hemodynamics due to hyperleaky angiogenic vasculature. In two distinct transgenic mouse tumor models, inhibition of ALK5 further enhanced vascular leakage into interstitium and facilitated increased delivery of high molecular weight compounds into premalignant tissue and tumors. Taken together, these data define a central pathway involving MMP14 and TGFbeta that mediate vessel stability and vascular response to tissue injury. Antagonists of this pathway could be therapeutically exploited to improve delivery of therapeutics or molecular contrast agents into tissues where chronic damage or neoplastic disease limits their efficient delivery. [less ▲]